Citadel has a broad spectrum of stations, spanning different locations, demographics and formats from country and rock music (classic or alternative) to talk and sports.
Three right panels from the top separately show ground spectra of three groups of stations in the polar cap, in cusp latitudes (~73° geomagnetic latitude) and in the auroral oval.
In the first step, we estimated a reference dispersion curve by fitting the zero-order Bessel function of the first kind to the observed cross-spectra of all station pairs at each frequency, thereby obtaining reference cross-spectra.
Blue axis marks the time window of waveforms used to estimate tremor locations (from 11 45 to 12 10) Fig. 4 (a) Waveform, (b) running spectrum, and (c) power spectra of UD component at station ROPW.
To compare the long-period ground motions in the Taipei basin generated from the great 2011 Tohoku-Oki earthquake (Mw = 9.0) and the 2008 Wenchuan (Mw = 7.9) earthquake, the acceleration spectra of horizontal component at station 101B generated by the two events are displayed in Fig. 9.
Only a small handful of stations existed, because spectrum was scarce.
For each station, the spectra of three directional components of the seismometer are shown for both radial and transverse linear sources that are synthesized by combinations of clockwise and anticlockwise rotations.
Figure 6 shows the power spectra of the horizontal components of both stations during nighttime and daytime.
Fig. S2: Average amplitude spectra of the vertical component recorded at station A306 and A109.
Discrete peaks were seen in the amplitudes of the spectra at all stations at frequencies below 10 mHz, as shown in Fig. 7.
